The present invention relates to a fluid filter, in particular an oil or fuel filter, of an internal combustion engine, having a filter housing and a cover detachably connected thereto, having a replaceable filter insert made up of a hollow cylindrical filter material body and two end plates enclosing said body at its ends, the filter insert being capable of being placed onto a central standpipe connected to the filter housing, the standpipe having at its free side facing the cover an end piece that is capable of axial displacement relative to the standpipe, the end piece being preloaded by a force acting in the direction of expulsion, and the end piece, when in its expelled position, being blocked by a locking device against insertion and a connection of the cover to the filter housing being prevented, and unlocking means guided by the filter insert being provided that, when the filter insert is placed onto the standpipe, actuate the locking device in the unlocking direction and allow insertion of the end piece. The present invention also relates to a filter insert for use in the above-named filter.
Increasingly high demands are made on fluid filters, in particular oil or fuel filters of an internal combustion engine, in particular with regard to filtering fineness and the durability of the replaceable filter inserts. These demands can be met only if suitable filter inserts are installed in the fluid filters. A fluid filter in which the installation of an unsuitable foreign filter insert is prevented during a filter maintenance including a change of filter insert is known from US 2003/0132158 A1. This document describes a fluid filter having the features named above. When an attempt is made to place into the filter housing a filter insert that does not have the required unlocking means, the end piece of the standpipe cannot be unlocked and pushed in. The filter insert then cannot be pushed sufficiently far into the housing, and a closing of the filter housing by the cover is excluded, because the cover is held at a distance from the filter housing by the expelled and locked end piece. In the case of an attempt to close the filter housing with the cover when no filter insert is put in place, the expelled, locked end piece also prevents the cover from being attached to the filter housing.
This known fluid filter does meet the demand of preventing the installation of an unsuitable foreign filter insert, but in order to accomplish this a relatively large number of individual parts is required, resulting in a high expense for production and assembly.